So there's some problems with re-establishing an encrypted channel. Usually I get a message telling me that bitlbee has to renegotiate the connection, but then I'm back in action.

Well, try it with two clients simultaneously connected...

If you're lucky the 3 clients will negotiate down to disabling the encryption. But normally they'll just engage in a mutual, infinite re-send loop...

Eh, if you have two clients connected, you're not being really secure, right?

Leaving that door open is bad juju.

I don't understand what you mean. How does having two clients connected rule out "being really secure"?

It seems insecure to leave another point of access open to the conversation, if merely out of principle, due to concerns over leaving a window open for eavesdropping.

There's no reason that has to be insecure (depending on your definition of "secure"). There's also no reason the user shouldn't be allowed to make that choice for himself.